Hi I am dr Kadhir, Most common cause of pain over the rib cage in otherwise asymptomatic child ( that is symptoms like cough, weight loss, difficulty in breathing ) is muscular pain. It may be due to heavy school bag or enquire about any trauma (fall), which kids usally hide in fear of saying to parents. Functional abdominal pain is a most common cause of pain in old children 6yrs. But this kind of pain is usually peri umbilical , recurrent , completely absent during sleep and wont be so specifically felt at the rib cage. Most often the pain resolves with analgesics and rest . If child is not improving then futher evaluation can be done.. Thank you for using healthcare magic.